There was spirit of gratitude and camaraderie as members of Parliament returned to work in the House of Commons Thursday, one day after a lone gunman killed a reservist and stormed Centre Block, sparking an hours-long lockdown.

Following a minute of silence, Prime Minister Stephen Harper crossed the floor to embrace Liberal leader Justin Trudeau and Opposition leader Thomas Mulcair. He then read a statement expressing thanks to the bravery of the House of Commons security staff, and vowing that Canada wouldn't be daunted by Wednesday's attacks.

"We will not be intimidated. We will be vigilant, but we will not run scared. We will be prudent, but we will not panic. Here we are, in our seats, in our chamber in the very heart of Canadian democracy, and the work is going on,” he said.

Later, during question period, Harper suggested that changes could be coming to laws that govern how Canada’s national security agencies track suspected extremists.

Mulcair asked what immediate measures are being taken to ensure security at Parliament and across Canada, and Harper replied that: “We are looking at various laws and options under the law to strengthen the ability to survey, detain and arrest individuals who are threats to us.”

In response to a question from Trudeau, Harper warned that “there are serious security threats in this country, and in many cases those serious security threats continue to be at large and not subject to detention or arrest.

“I know that is something that concerns Canadians, it concerns the government and we are working with the security agencies to determine how we can handle that situation.”

He later suggested that Canada’s security agencies “may need additional tools” to address the threat of suspected Canadian extremists.

Meanwhile, investigators are still trying to understand the chain of events that saw gunman Michael Zehaf-Bibeau shoot Cpl. Nathan Cirillo on the steps of the War Memorial, hijack a car on Parliament Hill and break into Centre Block before being shot and killed inside Parliament's Hall of Honour on Wednesday.

CTV News has confirmed that the hijacked car, a 2014 black Chrysler C30 four-door sedan, was registered to the Western Diversification Offices at 141 Laurier Ave. West.

Investigators are also trying to learn more about Zehaf-Bibeau, a Canadian with a lengthy criminal record who recently had his passport seized to prevent him from travelling abroad.

The Associated Press was able to speak with Zehaf-Bibeau's mother, Susan Bibeau, who said she is crying for the victims of the shooting, not her son. In a brief phone call Thursday, Bibeau said she did not know what to say to those hurt in the attack.

"Can you ever explain something like this?" she said. "We are sorry."

Sergeant-at-Arms honoured

After MPs filed into the House of Commons Thursday morning, Sergeant-at-Arms Kevin Vickers, the man credited with shooting the gunman, was given a rousing standing ovation  as he carried the mace and led a ceremonial parade into the chamber. He was greeted with enthusiastic and extended applause from MPs.

Vickers, who served 29 years with the RCMP before becoming sergeant-at-arms eight years ago, remained mostly stoical through the applause. At times, he appeared close to tears, eventually acknowledging MPs with several nods of thanks, and smiling when Harper came over to shake his hand.

Vickers has been hailed a hero for stopping the gunman who entered Centre Block Wednesday morning after fatally shooting a reservist at the National War Memorial just minutes before. The reservist, Cpl. Nathan Cirillo, was killed in the attack as he stood guard at the Tomb of the Unknown Soldier.

Earlier Thursday, Harper stopped to lay a wreath at the war memorial, along with several MPs. As the prime minister arrived, police were seen wrestling an unknown man to the ground, placing him in handcuffs and taking him away to a nearby police cruiser. It's unclear whether the man had tried to approach the prime minister.

Security remained tight around the memorial and Parliament on Thursday. The Parliament grounds remain closed to visitors, as are the streets around the war memorial.

Speaking from inside the House of Commons, CTV's Katie Simpson said it's an odd sight to spot security officers in front of the Peace Tower, instead of the usual throngs of tourists.

"There is always a visible security presence here, but today, you can see more officers on the front lawn and it's a bizarre scene to not see members of the public on the front lawn," she told CTV News Channel.

For several hours Wednesday after the shootings, the Parliament buildings remained under a lockdown while police searched for other suspects. Ottawa police said Thursday they were confident there was no second gunman in the attacks, but said the hunt would continue for possible accomplices.

"We're satisfied at this point that one individual was responsible for the shooting yesterday on the Hill," Ottawa Police Chief Charles Bordeleau told CTV's Canada AM Thursday morning.

He said there had been concerns Wednesday that there might have been a second person involved, which is why people were held in lockdown for so long Wednesday night.

"The threat is there. It was there before. And we all need to remain vigilant," he said.

Queen Elizabeth issued a statement to Canadians to say she was saddened by Wednesday's events.

"Prince Philip and I were shocked and saddened by the events in Ottawa yesterday. Our thoughts and prayers are with all those affected," she said in a statement through Governor General David Johnston.

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